Most aircraft that use datalinking/messaging equipment such as, for example, the Airborne Communications Addressing and Reporting System (ACARS) Management Unit (MU) or Communications Management Unit (CMU) systems have arrangements with more than one datalink service provider to provide the digital communication link between the ground host computer and the datalink system on board the aircraft. These service providers operate over several subnetworks, utilizing VHF, HF, and SATCOM links. Furthermore, each service provider typically operates on different VHF frequencies in different parts of the world.
The various service providers have different cost structures and different incentives to entice the aircraft owner/operators to utilize their services. As datalink and messaging services become more prevalent, the airlines are spending ever increasing amounts on these services, and are looking for ways to control costs. The system users also require that the datalink system provide an adequate and reliable means of establishing communications no matter where they are located on the globe.
A number of systems have been developed to optimize airline datalink costs, but each has drawbacks. In one such earlier system, regions were defined that incorporated a single longitude and latitude reference point to define a rectangular region. This earlier system limited flexibility in choosing among multiple providers with non-rectangular service boundaries. In addition, earlier systems were restricted to defining preferred VHF frequencies, and did not consider a regional preference for other subnetworks, such as HF, SATCOM and future subnetworks. Earlier systems also did not consider aircraft location or subnetwork preferences in the VHF frequency selection process. Each of the above limitations reduced the efficiency of the datalink/messaging system, resulting in non-optimum service choices.